An array of 32 microphones spanning 675 m of range was used to measure the frequency coherence for pulse signals propagating through atmospheric turbulence near the ground. Frequency coherence is the correlation between the fluctuations in received signals of different frequencies as expressed through the two frequency mutual coherence function evaluated at the same point in space and time. The experiments were conducted for frequencies between 200 and 1000 Hz under both downward and upward refracting propagation conditions. Measurements and theory are shown to be in good agreement for line-of-sight propagation. In the acoustic shadow region the frequency coherence bandwidth shows a strong dependence on mean frequency. The effects of refraction and diffraction, which cause wandering in the pulse arrival time and broadening of the pulse width, respectively, are clearly distinguished. The measurements provide experimental characterization of signal fluctuations for sound fields propagating outdoors. They are important for acoustic remote sensing and detection applications and for the validation of theoretical and numerical developments in sound propagation modeling.